Variable resistor with terminal structure



y 9, 1964 K. F. MILLER ETAL 3,134,085

VARIABLE RESISTOR WITH TERMINAL STRUCTURE Filed Aug. 17, 1962 FIG. 2

.IIIIIIII INVENTOR.

B KARL F SZOBQNYA ATTORNEY KENNETH E MlLLER United States Patent3,134,085 VARIABLE RESISTGR WITH TERMINAL STRUCTURE Kenneth F. Miller,Riverside, and Karl F. Szobonya, Anaheim, Calif., assignors to BeclimanInstruments, Inc., a California corporation Filed Aug. 17, 1962, Ser.No. 217,639 Claims. (Cl. 338-180) This invention relates to an improvedterminal structure for resistance elements and, more particularly, to aterminal structure for miniature resistance elements such as rectilineartrimmer potentiometers employing a base formed of a refractory material.

The present state of the art relating to rectilinear trimmerpotentiometers is highly developed as exemplified by the co-pendingapplication of James F. Gordon, Serial No. 584,008, new Patent No.2,845,679, entitled Potentiometer and Method of Manufacturing Same,filed May 10, 1956; the co-pending application of Jack E. Langenbach etal., Serial No. 166,054, entitled Improved Variable Resistor, filedJanuary 15, 1962', and the co-pending application of William J. H.Thoele, Serial No. 166,199, entitled Variable Resistance Device, filedJanuary 15, 1962. Each of the foregoing applications are assigned toBeckman Instruments, Inc., assignee of the present invention.

Conventional terminals for trimmer potentiometers comprise a rigid wireinserted through holes provided in the non-conductive base whichsupports the resistance element. The construction of a typical prior artterminal for a trimmer potentiometer employing a layer type resistancesuch as a layer of cermet resistance material preferably constructed inaccordance with the teachings of US; Patent No. 2,950,995, entitledElectrical Resistance Element, and U.S. Patent No. 2,950,996, entitledElectrical Resistance Material and Method of Making Same, each of whichare assigned to Beckman Instruments, Inc., is as follows:

The cermet resistance layer is preferably supported upon a base formedof a refractory material such as 'steatite or alumina having holesdrilled therethrough proximate the ends of the resistance element. RigidWires inserted through these holes are electrically connected torespective ends of the resistance element by a silver composition whichis silk-screened betwen the resistance element and the wire. Thiscomposition is fired to convert same to a continuous conductive metalfilm.

One diificult problem associated with this prior art terminalconstruction is that the wires are secured to the base by an adhesive orcement such as a glass cement which is fired simultaneously with thesilver composition. Prior to this firing step, it is necessary to firmlyretain the wire by providing an interference fit between the wire andits hole; otherwise, the wire may be dislocated during the silkscreeningstep. This interference fit, however, frequently results in fracture ofthe base element, particularly when the base is formed from a refractorymaterial.

Another problem associated with the prior art terminal structure is thesmall physical size of the components. Thus, for a typical trimmerpotentiometer, the holes in the base have a diameter in the order of0.03 inch. Placing small wires in such small holes is a very tedious,time consuming manual operation and is normally performed under amicroscope. This task is further complicated by the fact that because ofthe nature of the base material, the terminal receiving holes are notalways formed with uniform diameters, thereby necessitating tryingseveral wires of different diameters in order to obtain the requiredfit.

Accordingly, it is an object of this invention to provide support base.This 3,134,085 Patented May 19, 1964 ice a terminal for resistanceelements which may be firmly afiixed to a base of refractory materialwithout the need of adhesives or cements.

It is another object of the invention to provide a terminal structurewhich results in an interference fit between the terminal and its basehole without the necessity of employing different sized terminalstructures.

It is a further object of the invention to provide a terminal structurewhich will not fracture a base formed of refractory material wheninserted with an interference fit between the terminal and a hole formedin the base.

It is still another object of this invention to provide a terminalstructure which does not require extremely close tolerances, therebypermitting the devices to be easily and inexpensively manufactured.

Another disadvantage of the prior art rigid wire terminal structure isthat the wire provides a structurally weak member for attaching theretothe leads extending to the outside of the resistance element. During thesoldering or welding operation, the end of the wire terminal is oftenbroken off, thus necessitating discarding the entire element.

It is therefore another object of this invention to provide an improvedterminal structure providing a rugged structure for welding or solderingthereto electrical leads.

Other and further objects, features and advantages of the invention willbecome apparent as the description proceeds.

Briefly, in accordance with a preferred form of the present invention,there is provided a resistance support member having one or more holestherethrough proximate the resistance element. The terminal structurecomprises a headed pin formed from a malleable metal. The shank of thispin is serrated or grooved over a major portion of its length with asmall cylindrical portion at its outer end for facilitating insertingthe pin into the hole of the pin is then forced into the hole so as tophysically deform the serrations thereby rigidly retaining the pinwithin the hole without the use of cements or adhesives. A conductivematerial may then be silkscreened on the exposed end of the pin to makecontact -Wth the resistance element. The enlarged head of the invention;

FIG. 2 is an elevation View of a terminal pin constructed according tothe present invention;

FIG.'3 is'a plan view of the terminal shown in FIG. 2;

FIG. 4 is a partial sectional view of the terminal shown in FIGS. 2 and3 incorporated in the trimmer potentiometer shown in FIG. 1; and

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 4.

Referring now to FIG. 1, there is shown a trimmer potentiometer having asupport member 10 comprising a central portion 11 and upstanding endportions 12 and 13. Bearings 14 and 15 mounted in the end portions 12and 13 respectively, rotatably support a helically threaded adjustmentshaft 16. A movable contact block 17 is engaged by the adjustment shaftand is adapted to be translated along the central portion 11 of the bodybetween the end portions 12 and 13 upon rotation of shaft 16.

An elongated resistance element 20' and an elongated electricalconducting element (not shown) are mounted side by side on the centralportion 11 of the support member 10. Support member is preferably moldedor cast from a single piece of electrical insulating material, a ceramicsuch as steatite being a highly suitable material. The resistanceelement may be a wire wound resistor, a molded resistor, a depositedlayer resistor, or any other suitable type. A deposited layer type ofresistance element which is fired on a ceramic base is especially welladapted for use in the embodiment shown. Preferred deposited layerresistance elements comprise cermet resistance elements constructedaccording to the teachings of US. Patent Nos. 2,950,995, entitledElectrical Resistance Element, and 2,950,996, entitled ElectricalResistance Material and Method of Making Same. Similarly, the electricalconducting elements may take various known forms, a film of silver firedon ceramic being preferred.

Electrical contact means are carried on the contact block 17 forelectrically connecting a point on the resistance element 20 with theconducting element.

The foregoing described structure, including additional specific detailsthereof is described and claimed in the co-pending application of JamesF. Gordon entitled Potentiometer and Method of Manufacturing Same,supra.

The support member 10 incorporates respective holes 30, 31 extendingbetween the bottom and top surfaces of this member. Respective headedterminal pins 32 are retained in each of these holes for makingelectrical contact between end portions of the resistance element 20 andexternally extending leads 33 and 34. As shown,

these leads are attached to the head portion of the respective pins 32.These leads are preferably welded to the heads although other techniquessuch as soldering or conductive cements may be employed.

The terminal pin 32 is shown in the enlarged views of FIGS. 2 and 3.This pin is preferably formed from a malleable metal having atemperature coefiicient of expansion similar to that of the supportmember 10 and the electrically conductive silver layer. The pin mustalso resist firing temperatures of approximately 1000 F. to which it issubjected after its insertion in the support member. A representativematerial having the desired coefficient of expansion is an alloycomprising 29% nickel, 17% cobalt, iron, 0.5% manganese, 0.2% silicon,0.06% carbon, 0.10% aluminum, 0.10% titanium, 0.10% zirconium and 0.10%magnesium. The pin is preferably formed by a cold heading operationusing a die and punch in a manner well known in the art after which itis gold plated to prevent deleterious oxidation during a succeedingfiring operation. The pin may also be entirely constructed of a heatresistant alloy, examples of which are some stainless steels; platinumiridium alloy; platinum gold paladium alloy; platinum rhodium alloy; andan alloy comprising 76% nickel, 0.20% copper, 7.5% iron, 15.5% chromium,0.25% silicon, 0.25 manganese, 0.08% carbon, and 0.007% sulphur.

As shown in FIGS. 2 and 3, the terminal pin 32 cludes an enlarged headportion 36 integrally attached to a shank portion 37. A plurality oflongitudinal serrations 38 are provided on the surface of the shank 37,six being shown in the figure although more or less may be employed.

The portion 39 at the extreme end of the shank is formed as asubstantially cylindrical member for facilitating the insertion of thepin into the holes formed in the support base.

During the manufacture of the representative trimmer potentiometer whichis shown in FIG. 1, the support base 10 is formed with openings 30, 31and a resistance element 20 on its upper surface. Referring now to FIG.4, the pin 32 is inserted through the opening 30 until the top surfaceof the pin is approximately flush with the opposite surface of thesupport member. As shown, the bottom of the hole 30 is countersunk at 45to accommodate the taper of the terminal head 36. It will be apparentthat the cylindrical end portion 39 of the terminal pin will serve as apilot in cooperation with the countersink 45 to locate the terminal pin32 in the hole. As the pin is inserted further into the hole, thedimensions of the pin relative to the hole are such that the serrationswill be deformed, usually beyond the elastic limit of the malleablematerial of the terminal, but retaining sufficient residual resiliency,in cooperation with the minor resiliency of the base 10 to firmly holdthe terminal in position without the aid of adhesives or cements.

In order to achieve the desired attachment of the end to the resistancebase, the pin dimensions should be related to the diameter of the holeas follows: Referring to FIGS. 2, 3 and 5, the dimension A is the minordiameter of the pin and is the diameter of the outer pilot the hole.This insures that the pilot diameter of the pin is the diametricdimension of the serrated portion. The diameter of the hole in the baseelement is the dimension C. The dimensional relationship between thehole 30 and the terminal pin 32 must be such that the diameter A of theterminal must always be smaller than the diameter C of the hole, and themajor diameter B of the pin must always be larger than the diameter C ofthe hole. This insures thatt he pilot diameter of the pin willfacilitate inserting the pin into the hole while the serrations will bedeformed so as to rigidly retain the pin within the hole.

The next step in the potentiometer construction is that of electricallyconnecting the end of the pin 32 to the resistance element 20. Thisconnection is conveniently formed by silkscreening or otherwisedepositing a metallic terminating means 46 upon the surface of thesupport member 10 between the resistance element 20 and covering the endof the pin 32. This termination is preferentially a metallic pastecomprising 1%10% silver and %-99% platinum powders added to aconventional paste binder. The metallic paste is applied to a thicknessapproximating that of the resistance element 20 as shown in FIG. 4. Theassembly is again fired to convert the metallic paste to a continuousconductive metal film which tenaciously adheres to the base 10 andelectrically joins the resistance element and the terminal. The temperature coeflicient of expansion of the terminal pin 32 should be similarto that of this metal film so that heating of the resistance elementcaused by high ambient temperatures will not destroy the bond betweenthe film and the top surface of the pin. While other metallic pastes maybe employed, it is essential that the temperature required to convertthe metallic paste to a conductive film be lower than the temperature ofconversion for the resistance layer 20.

The electrical leads 33, 34 may then be joined to the head 36 of theterminal by soldering, welding or otherwise attaching leads thereto.Optionally, the terminal 32 may be formed with an elongated body (notshown) when, for example, the resistance element is to be mounted upon aprinted circuit board.

The terminal pin described above provides a greatly improved terminationfor resistance elements employing bases formed of a refractory material.The serrated construction is such that its maximum dimension (dimensionB) may be such as to form an interference fit with holes of severaldifferent sizes since the pin by nature of its being formed malleablematerial and its serrated construction deforms without causing afracture of the resistance base.

Another advantage of the invention is that the tolerances aresubstantially reduced since the major diameter B of the pin may vary (solong as the dimensional criteria described above are maintained) whilestill permitting its use in holes of different diameters. Thus, the

pin may be inexpensively manufactured in quantity by a non-precisiontechnique such as a cold heading operation.

Although exemplary embodiments of the invention have been disclosed anddiscussed, it will be understood that other embodiments may beconstructed employing the teachings of this invention. Thus, theserrated portion of the pin may be formed as longitudinal projections asshown and described, or, for example, they may be formed as a series oftangential projections making an oblique or right angle with thelongitudinal axis of the pin. Alternatively, the serrations may beformed as a helical thread or portions of a helical thread upon thesurface of the pin shank. Further changes, modifications andsubstitutions which may be made without departing from the spirit of theinvention will be apparent to those skilled in the art.

Also, other applications of the invention are possible. By way ofspecific example, the terminal will find wide application in anyminiature electrical component utilizing a refractory base element.

We claim:

1. A conductive termination for a resistance element comprising:

a support member for said resistance element having a hole extendingtherethrough proximate said rea sistance element, said hole having adiameter C;

a terminal for said resistance element which is rigidly retained to saidbase without any cement or adhesive including a pin formed of amalleable conductive material inserted in said hole, said pincomprising:

a generally cylindrical member of minor diameter A having a plurality ofserrations formed upon the outer surface thereof, the major diameter ofsaid terminal being B,

said dimension A being smaller than dimension C and said dimension Bbeing slightly larger than the dimension C wherein said serrations aredeformed upon insertion of said terminal into said hole;

and means electrically connecting said terminal to said resistanceelement.

2. The conductive termination defined in claim 1 wherein:

said terminal includes an enlarged head and wherein said hole formed insaid support member includes a countersunk opening opposite the surfaceupon which said resistance element is retained, said countersunkaccommodating said enlarged head;

said head providing an enlarged physical structure for facilitatingattaching electrical leads thereto.

3. The conductive termination defined in claim 1 wherein:

said terminal includes a cylindrical portion at one end thereof forproviding a pilot for locating said terminal within the hole formed insaid support memher. 4. The conductive termination defined in claim 1wherein:

said terminal is formed of a material having a temperature coeflicientof expansion similar to that of said support member and said meanselectrically connecting said terminal to said resistance element.

5. The conductive termination defined in claim 4 wherein:

said terminal is formed of an alloy substantially comprising 29% nickel,17% cobalt, 40% iron, 0.5% manganese, 0.2% silicon, 0.06% carbon, 0.10%aluminum, 0.10% titanium, 0.10% zirconium and 0.10% magnesium.

6. The conductive termination wherein:

said terminal is gold plated to prevent relatively high temperature.

7. The conductive termination wherein:

said terminal is formed of an alloy taken from the group consisting ofplatinum iridium alloy; platinum gold paladium alloy; platinum rhodiumalloy; and an alloy comprising 76% nickel, 0.20% copper, 7.5% iron,15.5% chromium, 0.25% silicon, 0.25% manganese, 0.08% carbon and 0.007%sulphur.

8. The conductive termination defined in claim 1 comprising:

a conductive paste applied over the exposed end of said terminal pin forelectrically interconnecting said resistance element to said terminal,said paste being subjected to a firing temperature for converting saidpaste to a continuous metallic layer, said terminal being constructed soas to be resistant against oxidation due to said firing temperature.

9. A variable resistor comprising:

a support means;

a resistance element mounted to the upper surface of said support means;

means for movably contacting said resistance elements, said meansincluding an adjustment shaft rotatably mounted upon said support means;

saidsupport means having first and second holes proximate the respectiveends of said resistance element; and

a terminal formed of a malleable conductor material inserted in each ofsaid holes, said terminal having a cylindrical end slightly smaller thanthe diameter of said hole and another portion provided with a pluralityof serrations which are deformed upon insertion of the pin within saidopening, the diameter of said serrations being such that the pin isrigidly retained within said hole without fracturing the support base.

10. The conductive termination for an electrical component comprising:

a support member for said electrical component, said member being formedof a refractory material and having a hole extending therethroughproximate said component;

a terminal formed of a malleable conductor material inserted in saidhole, said terminal having a cylindrical end slightly smaller than thediameter of said hole and another portion provided with a plurality ofserrations having a diametric dimension slightly larger than said hole,said serrations being deformed upon insertion of the pin within saidopening so that said pin is rigidly retained Within said hole withoutthe use of cement or adhesives and without fracturing the support base;and

means electrically connecting said terminal to said electricalcomponent.

defined in claim 5 oxidation under defined in claim 4 References Citedin the file of this patent UNITED STATES PATENTS 2,314,766 Bull et alMar. 23, 1943 2,962,691 Mande et al Nov. 29, 1960 2,997,679 Barden etal. Aug. 22, 1961 3,050,704 Dickinson et al Aug. 21, 1962 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent Noa 3,13%085 May 19 1964Kenneth F, Miller et alo error appears in the above numbered pat- It ishereby certified that the said Letters Patent should read as entrequiring correction and that corrected below.

strike out "the hole This insures that and insert instead portion lineColumn 4 line 2O the pilot diameter of the pin" 39 thereof. 'B" themajor diameter of the pin 28 for "thatt he" read that the Signed andsealed this 29th day of September 1964.

(SEAL) Attest:

EDWARD J. BRENNER ERNEST W.. SWIDER Commissioner of Patents AttestingOfficer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No3 134 O85 May 19 1964 Kenneth F Miller et a1 It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 4 line 2O strike out the hole This insures that the pilotdiameter of the pin" and insert instead portion 39 thereof "BM the majordiameter of the pin, line 28 for "thatt he read that the Signed andsealed this 29th day of September 19640 (SEAL) Attest:

EDWARD J. BRENNER ERNEST W. SWIDER Commissioner of Patents AttestingOfficer

9. A VARIABLE RESISTOR COMPRISING: A SUPPORT MEANS; A RESISTANCE ELEMENTMOUNTED TO THE UPPER SURFACE OF SAID SUPPORT MEANS; MEANS FOR MOVABLYCONTACTING SAID RESISTANCE ELEMENTS, SAID MEANS INCLUDING AN ADJUSTMENTSHAFT ROTATABLY MOUNTED UPON SAID SUPPORT MEANS; SAID SUPPORT MEANSHAVING FIRST AND SECOND HOLES PROXIMATE THE RESPECTIVE ENDS OF SAIDRESISTANCE ELEMENT; AND A TERMINAL FORMED OF A MALLEABLE CONDUCTORMATERIAL INSERTED IN EACH OF SAID HOLES, SAID TERMINAL HAVING ACYLINDRICAL END SLIGHTLY SMALLER THAN THE DIAMETER OF SAID HOLE ANDANOTHER PORTION PROVIDED WITH A PLURALITY OF SERRATIONS WHICH AREDEFORMED UPON INSERTION OF THE PIN WITHIN SAID OPENING, THE DIAMETER OFSAID SERRATIONS BEING SUCH THAT THE PIN IS RIGIDLY RETAINED WITHIN SAIDHOLE WITHOUT FRACTURING THE SUPPORT BASE.